Plug-in Solar Panels — Do They Make Cents?

An article over on CNET titled Got a deck? Solar panels now a plug-in appliance, suggests that you can buy from Amazon.com a 1,000 watt solar panel system that plugs into your wall outlet for only $1,099. I thought they were really on to something until I read the comments:

This article was written very poorly. At first read, it would appear that the 1,000 watt system costs $1,099.95, but going over to Amazon, that is just the price of one panel whose rating is 240 watts.

At about $4.58/watt, these panels will not produce electricity to pay for the finance charges alone. You will not be able to recover your investment on this, as the panels deteriorate through time.

If the 1,000 watt system costs $1,099.95, it would truly be disruptive as it will be feasible. But no, this solar PV will not cut it, still too expensive. If they can just sell these to about $2/watt, then it would be very worthwhile, given that you will mount these yourself.

On the other hand, I think this concept has potential (no pun intended). I bought a cheap solar inverter last year similar to the one in the above article just to experiment with. You connect one end to a solar panel and plug the other end into a wall outlet. The device converts your solar panel’s low voltage direct current into high voltage alternating current. Because the voltage (electric potential) from the inverter creates an electric version of back pressure against the voltage from the power company, it will reduce the amount of power coming into your house from the power line, which will slow down your electric meter, reducing your electric bill.

Modern homes tend to have significant phantom loads (appliances that draw a small amount of current even when you turn them off or when not in use): computers on standby, DVRs, televisions, motion sensors, the clock in your microwave and stove, tuners, routers, furnace, thermostat, chargers, and on and on.

Not many people have a thousand watts of phantom load so purchasing a thousand watt system would be a waste unless you plan to run things like the dishwasher, and clothes dryer etc. in sequence the whole time the sun is shining.

These inverters are intended to supplement your house power grid, not to spin your electric meter backwards. They will not send power (Volts times Amps) to your house wiring if there is no voltage coming to your house from the power company. This is to protect electricians who may be working on wiring inside or outside your house when the power is off. They of course, also won’t reduce phantom loads when the sun isn’t shining.

The inverter I purchased off Amazon cost about $100. It isn’t UL listed so I wouldn’t want to place it anywhere that might start a fire if it blew up. The one mentioned in the above article is, in theory, UL listed. I was testing one out just last week in my drive way. I had it plugged into a Kill-A-Watt to see how much power it was supplying for a given solar panel angle. A neighbor walking by asked how much it was producing. When I said “About 35 watts,” he suggested it would never pay for itself, and he was right. But then again, when did granite counter tops ever pay for themselves, or produce any power for that matter? A system like this could be viewed as a high-end appliance to reduce phantom loads.

I’m not recommending that people run out and purchase these because they are of questionable quality at this stage of their development, and I’m also not sure of their legality. I can envision a day when systems like this that cost less than a $ 1,000 might be (as insulation and double pane windows already are) required by building codes in sunny climates to reduce the impact of the significant and growing phantom loads. And who knows, if the price gets low enough, builders and home owners may start installing them to show off to neighbors.

By notKit P on May 20, 2012 at 9:15 pm

Russ just because something is required by a building code does not mean it is a good idea. Installing PV systems following code is a good idea just as relief valves are on hot water heaters.

I think I can make a very compelling argument for safety.

I would suggest that many energy savings code requirements are counter productive. For example, Russ does not need insulation or double pane wind because because he lives in a mild climate. Anyone who has ever used ‘phantom load’ in a sentence should get professional help.

We are planning a road trip to the PNW for our son wedding. We will stay at our friends’ house where I will get ‘phantom load’ explained to me. My wife says I have to be nice. Following the lecture, our male half of the family will invite me our to the garage-maljal to sample refreshments from the beer fridge.

He is a retired member of IBEW and understands the difference between power draw from an old fridge and ‘phantom loads’. We will look down in the valley at the nuke plant and speculate on the power level based on the cooling towers vapor and relative humidity. Columbia Generating Generating station just got approval to run for 60 years.

The 104 operating nuke plants is an example of a disruptive technology. Solar may have its usefulness but it will never be a disruptive technology because the nature of sunlight. For all those who advocate solar over concern about safety, do not forget about safety by saving money on a solar system.

Low flow shower nozzles are an example of energy saving code requirement that is hard to argue against because of the low cost and simplicity. PV is expensive and complicated. Each system must be engineered for the location.

Standby power, also called vampire power, vampire draw, phantom load, or leaking electricity (“phantom load” and “leaking electricity” are defined technical terms with other meanings, adopted for this different purpose), refers to the electric power consumed by electronic and electrical appliances while they are switched off (but are designed to draw some power) or in a standby mode.

“Insulation and double pane windows have a significant impact on heating bills in the Pacific Northwest. They have a significant impact on cooling bills in places like Florida. ”

That is not true. I have all single pane windows, lots of windows, and it does not have a significant effect on either heating or cooling bills because I live in a mild climate.

Let me explain the science for those who did not have the benefit of taking thermodynamics. The most efficient method of heat transfer is radioactive. In practical terms, properly designed roof overhands prevent direct sunlight from coming in windows in summer and allows the heat from the sun in in the winter assuming you have south facing windows. If you live in a cold climate, the most effective way to reduce heat loss through windows is with thermal drapes. The second most effective is low-e glass. The latter is my choice because I pick houses with beautiful trees around them instead of ugly houses. .

The second most efficient form of heat transfer is convection. In practical term, it does not matter how many panes of glass you have in a window if they are poorly fitting allowing lots of air to leak in. If air leak through the attic it will not matter how many inches of insulation you have. This is why weather stripping and caulk are very cost effective means to reduce energy use.

Finally, there is conduction or heat transfer through a material. The heat loss or gain is a function of the difference in temperature. My cooling bill is half of my heating bill because the air condition is 20 degrees below outside temperature in the summer and the heat is 40 degrees above outside temperature in the winter. When we lived in Michigan, the difference in temperature was 80 degrees in winter for many more days. Keep in mind that most building materials already naturally provide a certain amount of insulation.

So clearly, adding more insulation can significantly reduce energy bills in Las Vegas and Minnesota but not if you live in a mild climate.

High quality windows and door are important because the cost of replacement is high. The problem is that many builders cut corners with windows. While I think new windows should be energy efficient, poor quality windows will not maintain that efficiency very long. I would not replace well maintained wood windows just to save energy.

Personally, I think the bootleg scheme is fine, but if you want to DIY a code approved system, its really not a whole lot harder and not all that expensive. I used the Enphase micro inverters and installed the system myself with permit and utility company approval and net metering — no serious hassles, but Montana may be a bit more relaxed than some places. Its probably not a good first wiring project, but if you have done some wiring already, its not that complicated. This is my system: http://www.builditsolar.com/Projects/PV/EnphasePV/Main.htm I’ve heard from a number of others who have done similar systems. At todays prices the before rebates cost for all the parts is about $2.50 an STC peak watt.

If the main goal is to save money, there are lots better ways to go — this is our experience on PV vs other energy cost saving: http://www.builditsolar.com/Projects/PV/EnphasePV/Economics.htm See the “How does PV compare to other soalr or conservation projects” heading. Other good DIY conservation/solar projects still beat PV by a factor of 10 or so.

Another great use which I have found for the system which you have described is to use the cells to charge the battery in our camper-trailer while spending days in the remote wilderness of Idaho. It can maintain a full charge on the battery while powering the many uses of our trailer.

I’m not sure where Notkit P is going with his comments….. You can easily save anywhere from $126–$465 a year when replacing single-pane windows with double-paned, no matter where you live in the continental USA.

To have a full understanding of why this is, a basic knowledge of “Thermodynamics” as stated by is not sufficient, you must have a full understanding of Heat Transfer and transient heat conduction. The main problem with single-paned windows with “Thermal Drape” as stated above, is that depending on relative humidity, condensation will occur on the inside of the window inbetween the window and the thermal drapes, causing issues with wood and potential mold problems. Using multiple-paned argon filled windows will prevent this problem.

A simple example: a small .8m x 1.5m single paned window will lose on average about 266 Watts of energy while it is slightly below freezing outside, and condensation will form on the inside of the window. The same sized double-paned window will only lose 69.2 Watts, while the inside surface of the window stays above the condensation temperature and stays dry.

It is more of an economics problems than an engineering problem. I have beautiful single pane wood windows in my present house. When I built my dream house in the California foothills I used the best expansive double pane wood windows I could find. The ‘state’ told me I had too many windows. Thirty-seven pages of calculations later I show how I met Title 24.

So while beautiful and efficient windows are expensive, the most expensive windows are not necessarily the best.

The economics are different for replacing well maintained and attractive single pane wood windows with similar in appearance with more efficiency double pane windows. The pay back period is terrible.

I am a mechanical engineer and am very good at having much lower utility bills than other in a particular area. My present house in mild climate did not have significant energy costs when I bought it but it did have some comfort problems. I fixed the attic ventilation problems, added weather stripping and radiant barriers which also served as a better fire barrier system. Then we added a new heat pump.

I have done the calculation, replacement double pane windows in a mild climate fall into the category of diminishing returns.

Worse than that is that I know of many who have been scammed by replacement window con artists.

What is the cost, what is the pay back period? Do not sign a second mortgage without the answer to those questions.

“Insulation and double pane windows have a significant impact on heating bills in the Pacific Northwest. They have a significant impact on cooling bills in places like Florida.”

NOTKITP responds [in part] with:

“That is not true. I have all single pane windows, lots of windows, and it does not have a significant effect on either heating or cooling bills because I live in a mild climate.”.

I think this is a perfect example of why many people do not enjoy blogging with NOTKITP. Even thou the statements made by MECHENGR are well written, backed up with data to make a point and are generally accepted engineering principles, NOTKITP seems to think it is his responsibility to point out; “That is not true.”.

I don’t know if NOTKITP is just that insensitive to what others post or just feels like he must try and make someone else look bad. But to say “that is not true” is like calling a fellow engineer a less than desirable name.

Everyone can read the statement made by that engineer and see that the statement already contains variables [$ values] which allows for the various climate conditions in the U.S. But to say the posting is “not true” is inappropriate. The engineer did not say “this is always true” or dual pane windows will “always save money”.

That is why I no longer respond to comments made by NOTKITP and won’t until he learns to be considerate of fellow bloggers. It is certainly o.k. to point out errors or omissions in an appropriate manner, but to infer that only his comments are of value shows the type arrogance I find distasteful.

I do wonder at the “it will never pay for itself” attitude many offer as to solar panels, electric or hybrid cars. I have a hybrid car and compared to the vehicle it replaced I use 1/3 of the fuel bill. This is substantial. No car ever pays for itself, gas, Diesel, hybrid, electric. While you can compare with anything you can make an argument about anything and come up with negative factors. But if I rather buy a 30K Nissan Leaf, vs a 30K Lexus my numbers tell me I shall pay out considerably less per mile driven by using Leaf. No service at all for oil, filters, coolant, transmission, exhaust repair, engine upkeep, etc. Substantial also is the effect of supplies, fuel, packaging for products, etc. I just installed 24 solar panels on the roof. I also get the “It will not pay for itself” comment. Well, I see this differently. I get a return in investment not available right now for my dollars. Just use Google photos to see how solar panels are contributing to the environment, the finances of business and people and to the economy. Ever heard the comment in reference to laptops or smartphones? Why does a 12 year old need a $700 a year smartphone for? It will never pay for itself!!

I can’t disagree with anything you said. We are all loathe to admit to ourselves that status seeking drives much, if not almost all, of our daily energy expenditures. We are at heart a social primate and status within our troop has been, through 99% of our evolutionary history, a deciding factor in successful propagation of our genetic legacy. I know. You don’t do anything in the name of status, and why everyone says that, remains, to date, an unsolved mystery ..land my apologies for the excessive punctuation;.

The never pay for itself idea is stupid. Of course with just one panel you’re not going to be making a significant amount of energy or payback. Add more panels!

I have been piloting a project here in the California high desert using PNP inverters exactly like this to show just how ideal they are for consumers to reduce their electric bills. At the pilot location, mid day, the meter stalls out at 0 kWhrs for a solid hour. This is only with (4) 100 Watt cheap panels purchased off eBay. The net result is that the electric bill at the pilot location is only $27 a month. Granted, the homeowner uses probably less electricity than the average household because she handwashes her dishes and hangs her clothes out to dry instead of using a clothes drier, but I will let the results speak for themselves. During daylight hours, it pays for all fantom electricity usage and then some. If a net-metering agreement was in place with Edison, during peak hours, there would be in fact a slightly negative billing each day. And the 600 Watt PNP inverter used has room for two more panels still before maxing out on paper. Realistically it could take three more because panel output is never what panels are rated at. Anyone interested can see results posted on my facebook (NoNameSolarCompany)…

The real problem with this technology inhibiting mass uptake is that it is not UL or ETI or other laboratory certified to comply with national electric code. Because of this, it can never be used to deploy panels on any project needing building permits nor will most insurance companies cover damage if any damage is caused by the device that is not “UL approved”.. That’s the only real obstacle here from making these things fly off the shelves.

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Russ Finley is an avid amateur naturalist. He is also an aerospace engineer with a Bachelor of Science degree in Mechanical Engineering, an Associate’s in Aviation Technology, airframe and power plant mechanic’s licenses, and pilot’s license, all from Purdue University.